(1) Field of the Invention
The present invention relates to insulators adapted to be used for supporting transmission lines or the like and particularly having excellent water-repellency recoverability.
(2) Related Art Statement
So-called polymer insulators are each constituted by covering the outer periphery of a core member made of an FRP with shed portions made of silicone rubber. It has come to be known that such polymer insulators exhibit large effects such as prevention of corona noise and flash-over in polluted environments due to excellent water repellency of silicone rubber.
In general, shaped bodies made of polymer materials exhibit water repellency at an initial use stage. However, there is a drawback that when such shaped bodies are used outside, they lose their water repellency in a relatively short time due to irradiation with solar beams (ultraviolet rays). On the other hand, it is known that fluorine resins represented by Teflon, silicone rubber and silicone resin are strong against ultraviolet rays.
However, when even fluorine resin or silicone resin is used as a covering material for high voltage insulators, their water repellency is unfavorably lost with the lapse of time by being exposed to partial discharging at the surface thereof, and pollutants attached onto the surfaces. Some researchers reported, however, that although silicone rubber among the above materials tentatively loses water repellency when the surface is exposed to partial discharging or attached with pollutant, such silicone rubber recovers its water repellency after that (for example, after 24 hours). This is a fact that the inventors also confirmed.
Although the mechanism by which this water-repellency is recovered has not been clarified, certain researchers explain that this mechanism is based on the phenomenon that a low molecular silicone component contained in silicone rubber gradually oozes out with the lapse of time. The present inventors have confirmed this through various experiments, and support the above explanation.
Such a kind of the low molecular silicone Component is not a component positively added into silicone rubber, but exists in only an extremely small amount as a byproduct produced in the production step of diorganopolysiloxane, which is used as a main starting material for silicone rubber. For this reason, there is a problem that the low molecular silicone component is being exhausted as the use time period increases, so that the time required to recover water repellency increases, and the effects of preventing the corona noise and flash-over in the polluted environments become smaller.